Viscoelastic properties of liquids, in particular including those with complex flow behavior (such as for example non-Newtonian fluids), are usually measured in the laboratory, for example with the aid of oscillating viscometers. The oscillating properties of an oscillating body under the influence of the viscous liquid are in this case measured up to a frequency of several hundred hertz. To determine the viscosity, it may be necessary to know the density of the liquid or measure it at the same time.
In process measuring technology, MEMS components or oscillating quartz crystals, which typically operate at much higher frequencies, such as for example at several megahertz in the case of TSM oscillating quartz crystals (TSM stands for: “thickness shear mode”), are used as viscosity sensors for the online monitoring of processes. For this reason, viscosity sensors that are available at present for process measuring technology are mainly used in the monitoring of simple (Newtonian) liquids, the viscous behavior of which can be described by a single viscosity parameter (for example the dynamic viscosity r). However, the measurement results achieved with such sensors at high frequencies for the viscosity of non-Newtonian fluids often cannot be compared with reference values determined in the laboratory.
In the latest developments it is being attempted to use spring-mounted oscillating plates produced by semiconductor technology at lower oscillating frequencies (to about 16 kHz) for viscosity measurement, the oscillating amplitude being measured with the aid of piezoresistive silicon layers. However, such sensors are complex to produce and, among other things, present difficulties with conducting liquids.
The object on which the invention is based is to provide a sensor arrangement that can be used in process measuring technology for measuring physical properties of liquids, in particular viscosity, which is easy to produce and which can be operated at such low frequencies that the measured values achieved can be compared with conventionally determined laboratory values.